Briefly five RAS, consisting of a mechanical particle filter, moving bed biofilmreactor and a foam fractionator using compressed air, were stock with 18 juvenile turbot each. At the start RAS were filled with 300 l disinfected sea water (salinity of 26 g/l) and five mixtures, contain-ing same ratios but different amounts, of ZnSO4·7H2O, MnSO4·H2O,CoSO4·7H2O, CuSO4·5H2O and FeSO4·7H2O were added to obtain